Examples

Explore Roc through small, runnable examples.

Getting started

• Hello, World! — Print a greeting with a minimal Roc application.
• FizzBuzz — Use conditions and arithmetic to solve the classic FizzBuzz exercise.
• All Syntax in 1 File — Explore the language syntax in one annotated file.

Types and functions

• Tuples — Group values of different types into tuples and access their elements.
• Pattern Matching on Lists — Match list shapes and bind their elements to names.
• Custom Inspect — Customize how opaque values appear when inspected, including hiding a secret.

Collections and iteration

• Basic Dict Usage — Create a dictionary and look up, insert, and remove entries.
• Looping Effectful Functions — Repeat an effectful operation by reading and summing numbers until input ends.

Error handling

• Error Handling Basic (Try) — Represent success and failure with Try and handle both outcomes.
• ? Operator Desugaring — See how the ? operator expands into explicit error handling.
• Safe Math — Handle arithmetic overflow and other numeric errors explicitly.
• Error Handling Real World (Try) — Combine error handling across several operations in a command-line program.

Parsing and encoding

• JSON — Parse JSON data into a typed Roc record.
• Encoding & Decoding — Define custom encoders and parsers for a nominal type.
• Record Builder — Build a date parser by combining field parsers with record builder syntax.

Programs and algorithms

• Least Squares — Find the smallest integer whose square exceeds the previous square by more than 1,000.
• Towers of Hanoi — Solve the Towers of Hanoi puzzle with recursion.
• Graph Traversal — Represent a graph and traverse its connected nodes.

Organizing code

• Import Files — Embed text or binary files in an executable at compile time.
• Multiple Roc Files — Split an application into modules across multiple files.
• Import from Directory — Import a module from a subdirectory.
• Import Package from Module — Pass a package dependency from an application to one of its modules.

Packages

• Random Numbers — Generate reproducible pseudorandom numbers with the roc-random package.
• Parser — Compose a parser that counts letters using the roc-parser package.

Platforms

basic-cli

• CLI Args Simple — Read arguments passed to a command-line application.
• CLI Args File — Open a file named by a command-line argument and read its first line.
• Terminal Commands — Run an external command and work with its output.
• Snake Game — Build a playable Snake game with an effectful game loop.

These examples are built and tested with Roc nightly-2026-10-09-258ab27, unless noted otherwise.

Their source comes from roc-lang/examples at 0457fea.